1. Field of the Invention
The present invention is related to a liquid crystal display device in which light emission from viewer""s side (display side) of a liquid crystal layer is turned ON/OFF or controlled to be increased/decreased on the basis of a birefringence (double refraction) effect of the liquid crystal material.
2. Description of the Related Art
Liquid crystal display devices have excellent features such as thin and light weight, low power consumption and mild fatigue in eyes. For this reason, the liquid crystal display devices have come to be used in various fields such as displays for notebook-size personal computers and for portable wordprocessor-dedicated machines, and is expanding their fields of use and markets more and more.
In recent years, not only the market of medium/small screen-sized liquid crystal display devices expands continuously, but also the market of large screen-sized (larger than, or equal to 13 inches) liquid crystal display devices expands rapidly. As for the large screen sized liquid crystal display devices, reduction of viewing-angle-dependency in a color tone and contrast is a requirement to meet. Particularly for large screen-sized computer displays for CAD system and the like, and for displays for conference or interview purposes, reduction of the viewing-angle-dependency is an important requirement.
As one of the methods for reducing the viewing-angle-dependency, liquid crystal display devices utilizing the birefringence effect of liquid crystal materials, in particular, IPS (In-Plane Switching) type liquid crystal display devices are researched and developed eagerly.
Referring now to a schematic diagram of FIG. 5, a basic displaying mechanism in an IPS type liquid crystal display device will be explained. In following, an IPS type liquid crystal display device operated in a normally black mode is exemplified.
Liquid crystal molecules are oriented to be substantially horizontally with respect to a plane of the substrate, and to be in substantially parallel to each other. A polarizing plate 15 is arranged on an outer surface of an array substrate 2 (namely, on lower surface of lower board in FIG. 5), while another polarizing plate 28 is arranged on an outer surface of a counter substrate (namely, on upper surface of upper board in FIG. 5) which is provided on a screen side or viewer""s side. The arrangement is made in such a manner that polarizing directions of these polarizing plates 15 and 28 are intersected substantially perpendicular to each other.
At an initial stage (non-voltage-applied state), as represented in a left half portion of FIG. 5, the liquid crystal molecules are arranged to be substantially parallel to the polarizing direction of the lower polarizing plate 28. As a result, light from a light source at underneath is not transmitted to viewer""s side, that is upper side in the figure.
On the other hand, as shown in a right half portion of FIG. 5, in a domain of each of pixels (minimum display unit) on the array substrate 2, when a voltage is applied between a pixel electrode 21 and a counter electrode 22, on orientation (director direction) 5 of liquid crystal molecules are controlled to be aligned along lines of electric force, so that the light is transmitted on basis of the birefringence effect.
Ordinarily, to perform a color representation, colored patterns constituted by fine patches of red (R), blue (B), and green (G), which are three primary colors of light, are formed on the counter substrate 1. This colored pattern called as a color filter is formed in such a manner that colored films of the three primary colors are allocated every three pixels located adjacent to each other. Then, relative ratios of light intensities as to these three pixels located adjacent to each other are adjusted, so that color tone representation can be realised. There are frequent occasions when a set of 3 minimum display units, i.e., R, G, D is counted as a 1 pixel in color display devices. However, in this specification, a minimum display unit is referring to as a xe2x80x9cpixelxe2x80x9d.
The color patterns of three primary colors are formed in the following manner. A coating material in which any one of primary color pigments has been dispersed is coated on a whole surface of the substrate by way of either a spin coater or a curtain coater. Subsequently, a patterning process in use of photolithography technique is carried out so as to form colored films only over pixels that are allocated to this selected color of the three primary colors. A similar patterning process is carried out with respect to other primary colors. In this way, colored patterns of the three primary colors are obtained by 3 times of the coating and patterning processes.
On the other hand, in order to make a uniform thickness of liquid crystal layer, spherical resin bodies having uniform diameters are dispersed on any one of the substrate boards before the array substrate is attached to the counter substrate. This spherical resin body is called as a xe2x80x9cspacerxe2x80x9d.
However, these spherical spacers are partially aggregated, in the worst case, a bright-point defect is produced on the screen of the liquid crystal display device. Further, when fluctuation and deviation in dispersing density give rise a region of substantially no spherical spacer, the thickness of the liquid crystal layer in this region becomes thinner than that of another region. Thus, the resulting contrast ratio on the display screen would become unequal, to deteriorate the picture representation on the screen. Additionally, since the spherical spacers are distributed also to the display areas within the pixels, light leakage will occur by these spherical spacers themselves, and by the orientation failures of the liquid crystal molecules at around the spherical spacers. Such light leakage deteriorate the contrast ratio.
Usually, each of these colored films of three primary colors, which constitute colored patterns, is formed separately in respective process step. As a result, it is difficult to achieve sufficiently uniform thickness. In most cases, a stepped portion is produced between a color-film region of a certain primary color and an adjacent color-film region of another primary color. That is, a height difference in respect of a surface of the substrate is produced between these regions.
More specifically, in order that a color representation characteristic of a liquid crystal display device may be improved so as to substantially represent a natural color, a thickness of a colored film used to form a colored pattern must be made thick, so that color density of the colored pattern is increased. However, when the thicknesses of the respective colored films of the three primary colors are increased as a whole, the differences in the thicknesses among the regions of the colored films are also increased. Usually, a thickness of a colored film is required to be about 1 xcexcm. In this case, fluctuations in thickness is up to about 0.2 xcexcm.
In the case that a thickness of a colored film is made thicker than 1 xcexcm, fluctuations in thickness would be further increased. This is because in such a coating apparatus as a spin coater and a curtain coater, a coating materials for colored film having a high content of pigment and having a high viscosity cannot be sufficiently uniformly distributed on a substrate board.
The larger, the size of the substrate board on which the colored patterns are formed is, the bigger the fluctuation in the thickness of such colored films becomes.
Deterioration of the display performance due to uneven thickness of the liquid crystal layer is especially intense in the liquid crystal display devices which utilizes the birefringence effect of the liquid material as a display mode. As mentioned previously, the thicknesses of the liquid crystal layer has been made uneven because of the fluctuation and deviation in the distribution of the spherical spacers and because of the fluctuation in the thickness of the colored films.
The present invention has been made in view of the above-mentioned problems, and is to provide a liquid crystal display device in which light ray through the liquid crystal layer is controlled on the basis of the birefringence effect of a liquid crystal material, capable of reducing a thickness fluctuation of liquid crystal layer and therefore, capable of avoiding an occurrence of a portion of a display image deterioration such as a deviation of contrast ratios.
A liquid crystal display device, according to the first aspect of the present invention, is featured by such a liquid crystal display device comprising: a first substrate having a color filter layer on a first insulator substrate; a second substrate opposing to said first substrate; a spacer projection integrally formed on at least one of said first substrate and said second substrate and keeping a predetermined gap between the substrates; a liquid crystal layer held in said gap; and a plurality of pixel regions performing a display operation based on the birefringence effect of said liquid crystal layer; wherein: the color filter layer is a resin layer which is formed on said first insulator substrate and is tinted with requested colors corresponding to said pixel regions.
With employment of such a structure, there arises no deterioration in the display performance associated with uneven distribution and agglomeration of spherical spacers. Further, the deterioration associated with uneven thickness of the liquid crystal layer is largely reduced.
A liquid crystal display device, according to the second aspect, is featured by that the resin layer is a layer formed of a dye-accepting material onto which each dye has been discharged and accepted in correspondence with respective ones of said pixel regions.
With employment of the above-explained structure, an integrated color filter layer can be easily formed in low cost.
A liquid crystal display device, according to the third aspect, is featured by that the first board contains a light shielding film arranged at a peripheral portion of the pixel region; and the spacer projection is provided within a region corresponding to the light shielding film.
With employment of such a structure, it is possible to avoid lowering of the contrast ratio and lowering of the aperture ratio, which are caused by the light leakage due to the spacer material itself, and by failed-orientation of the liquid crystal at around the spacers.
A liquid crystal display device, according to the fourth aspect, is featured by that the spacer projection is directly provided on a layer of the dye-accepting material.
With employment of such a structure, since the spacer projections are formed on a plane having a little undulation, distance between the boards can be controlled in a more uniform manner.
A liquid crystal display device, according to the sixth aspect, is featured by that the spacer projection is formed of transparent light-curing resin.
With employment of such a structure, it is possible to readily form the spacer projections having an equal dimension in projecting-wise direction.